Ovualtion test

Danielle • Praying for a baby ❤️✨
Ok so I am new the take opks I have done a few and the first few had a slight second line which I know isn't positive. But today I just took one and there is not any second line. I am so confused! Why would I get a faint second one twice and then none the 3rd I am only on cd 12 if that means anything. Does anyone know why?